Fuel delivery pumps are both flowed through by the fuel for delivery and flowed around by the fuel. Fuel delivery pumps used in motor vehicles have electric motors which are used for driving the delivery stage, which is formed for example by a pump impeller. To ensure safety with regard to electrostatic discharges (ESD), the electrically conductive elements of a fuel delivery pump must be grounded. This serves for preventing short-circuits and thus the formation of sparks, which could lead to ignition of the fuel. Furthermore, the functionality of the fuel delivery pump may be impaired as a result of the generation of electrostatic discharges. The parts that must be grounded include in particular the pump stage, the housing of the fuel delivery pump and the motor housing, in which the rotor and the stator of the electric motor are arranged.
At the same time, it is necessary to prevent the shaft of the fuel delivery pump, on which the delivery stage is arranged, from being short-circuited with the negative pole of the voltage supply or with the ground potential, and thus likewise being grounded. Such a short circuit may lead to failure of the fuel delivery pump or to undesired deposits on the shaft or on the rotor, in particular in the vicinity of the carbon brushes. This may lead to an impairment of the service life of the fuel delivery pump.
Various devices are known in the prior art which present possible solutions to the problem. Accordingly, fuel delivery pumps are known which have additional resistances for realizing adequate grounding or decoupling. Fuel delivery pumps are also known which have a pump stage composed of plastic, whereby insulation of the shaft may be achieved. Furthermore, fuel delivery pumps are known which provide grounding of the motor housing and thus also grounding of the shaft.
A disadvantage of the devices in the prior art is in particular that either no sufficient safety with respect to electrostatic discharges may be achieved, or the grounding of the motor housing also generates grounding of the shaft, whereby deposits may form in the interior of the electric motor. The embodiment of the pump stage as a plastics component leads to lower stability and thus a shortened service life.